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Utility pipes in trenches

Cables

Cables are vulnerable to harsh treatment and the main causes of malfunctions are:

• Damage to the coating
• Pulled connections
• Narrow curves

A lot of emphasis is therefore placed on handling utility pipes carefully in open trenches. Care must be taken to ensure the coating is not damaged, connections are not pulled and that the curves in the pipes are not too tight.

Handling and structure of oil pipes

Oil pipe structures are very sensitive to harsh treatment. In trenches where structures of this kind are being excavated, there is a need to clear the earth material from them, reinforce them or bind them to avoid any strain on the conductor joints and the cable itself.

Storage in wooden casing or plastic tubes

When there is a need to temporarily move utility pipes in trenches for keeping, they have to be fixed up on wooden ducts or plastic tubes which are hung up on bridges, pegs or solid fittings at least half a metre from the edge of the trench. Use a clips of a minimum diameter of 8 mm, and at least 10 mm when the water pipelines are tied up. There should be no more than 3 m between suspended electric cables when plastic tubes are used. When heavy water pipes are tied up, the hanging brackets should be at 12 m intervals. When digging under thicker pipes, contact us about how they should be stored during the construction period.

Storage of utility pipes that cross the trench

Since utility pipes cross the trench they need to be tied up on a beam that needs to be as sturdy as the trench is wide.

Storage of utility pipes in a curved trench

When handling utility pipes in curved trenches, particularly with electric cables, they need to be tied up with tighter pegs than those used in straight trenches and there can be no more than 1 m between each peg.

The long-term storage of utility pipes should be in sealed wooden ducts.

When the aforementioned utility pipes are stored for a long time they should be kept in closed wooden ducts. Particular care must be taken to lay sand around the pipes where they enter the ducts and to secure the stability of the ducts with braces. A special contract must be made with Veitur Utilities for the long-term storage of utility pipes in wooden ducts.

Curves in the pipes

Curves in cables should always have a turning radius that is bigger than fifteen times the size of the cross section of the cable. The picture shows how to evaluate how much the cable can be bent.

• Typical supply lines are 2 cm in diameter and the turning radius can therefore be 30 cm.
• A typical consumer cable has a diameter of 3.5 cm and the turning radius therefore cannot be less than 55 cm.
• A typical high-voltage cable has a diameter of approximately 6 cm and the turning radius therefore cannot be less than 1 m.

Oil pipes are very sensitive to rough handling in open trenches and the curve should therefore move as little as possible.

Welded plastic pipes

Nowadays thinner cold water pipes are laid in plastic pipes, which are welded together and can withstand considerable pulling, but pipes that are assembled with joints should be handled the same way as electric cables in trenches.

Veitur Utilities’ new household pipelines, i.e. hot and cold water pipes as well as the electric supply line, are laid in solid plastic pull-through conduits from the property boundary to the house.

The fibre optics cable of the Reykjavik Fibre Network is laid in an orange pull-through conduit.

Reinforced iron pipes/ductile

Reinforced iron pipes or ductile pipes, as they are more frequently called,are not welded together, but rather laid in straight paths between brackets. These pipes cannot be left suspended in the air, unless in consultation with Veitur Utilities. Care must be take to ensure there is no excavating around their corners and joints. These pipes tolerate very little pulling because there are only rubber seals around their joints.

Steel pipes

Most district heating pipes are insulated steel pipes in plastic coating. These pipes are not flexible and care must be taken to ensure they do not move too much when they are suspended in the air. Support has to be built under them when they have been excavated around.

Crossing cables

Under roadways, driveways and wherever applicable, the plastic pipes that are laid for pulling through underground cables are most often red. The pipes are 50 mm for thin cables, 110 mm for thick cables and 50 mm for fibre optics cables. It is important to place enough sand between the pipes to ensure they do not lie beside each other when the trench is refilled.